Fix contradictions between the documentation, the README, and the library (#5825)

- Discarded values: the legacy macro only changes <= and >=; != is true by default
- Out-of-range numbers are rejected while parsing, not stored as NaN
- merge_diff round trip: point to the ordered_json caveat
- ensure_ascii example shows the escaped output
- out_of_range.405 is thrown for "remove"/"move" on the root, not "add"
- CBOR stores binary subtypes as tags
- Integer/float comparison uses exact values, not conversion
- diff, flatten, and the binary writers are depth-bounded
- FAQ: max_digits10 for serialization, trailing commas are supported
- out_of_range.407 is still thrown by to_bon8
- FetchContent_MakeAvailable needs CMake 3.14
- json_fwd.hpp contents, operator< link, RFC 7396 for merge patch
- README: dump() wording, merge_diff, MSYS2/build2, patch comment typos,
  operator[] link, embedded CMake example aligned with the docs

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/index.md

@@ -85,7 +85,7 @@ The class satisfies the following concept requirements:
 - [EqualityComparable](https://en.cppreference.com/w/cpp/named_req/EqualityComparable): JSON values can be compared with
   `==`, see [`operator==`](operator_eq.md).
 - [LessThanComparable](https://en.cppreference.com/w/cpp/named_req/LessThanComparable): JSON values can be compared with
-  `<`, see [`operator<`](operator_le.md).
+  `<`, see [`operator<`](operator_lt.md).
 - [Swappable](https://en.cppreference.com/w/cpp/named_req/Swappable): Any JSON lvalue or rvalue of can be swapped with
   any lvalue or rvalue of other compatible types, using unqualified function `swap`.
 - [NullablePointer](https://en.cppreference.com/w/cpp/named_req/NullablePointer): JSON values can be compared against

docs/mkdocs/docs/api/basic_json/merge_diff.md

@@ -11,7 +11,7 @@ added members with their new values, and removed members with the value `#!json
 member by member; any other value that differs, including an array, is replaced as a whole.
 
 For two JSON values `source` and `target`, where `target` contains no object member whose value is `#!json null`, the
-following code always yields `#!cpp true`:
+following code always yields `#!cpp true` (for [`ordered_json`](../ordered_json.md), see the notes below):
 ```cpp
 basic_json patched = source;
 patched.merge_patch(merge_diff(source, target));

docs/mkdocs/docs/api/basic_json/number_float_t.md

@@ -52,9 +52,10 @@ With the default values for `NumberFloatType` (`double`), the default value for
 > interoperability can be achieved by implementations that expect no more precision or range than these provide, in the
 > sense that implementations will approximate JSON numbers within the expected precision.
 
-This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values
-smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally
-and be serialized to `null`.
+This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note that
+numbers smaller than `-1.79769313486232e+308` or greater than `1.79769313486232e+308` are rejected during parsing with
+[`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406). Non-finite values (NaN and infinity) can
+only be stored by assigning them directly and are serialized to `null`.
 
 During deserialization (from JSON text or any of the binary formats), a finite number that does not fit into
 `number_float_t` is rejected with [`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406), for

docs/mkdocs/docs/api/basic_json/operator_eq.md

@@ -20,7 +20,8 @@ bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
 1. Compares two JSON values for equality according to the following rules:
     - Two JSON values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored
       values are the same according to their respective `operator==`.
-    - Integer and floating-point numbers are automatically converted before comparison.
+    - Integer and floating-point numbers are compared by their exact values, without converting the integer to
+      floating-point. For instance, `9007199254740993` and `9007199254740992.0` are not equal.
 
 2. Compares a JSON value and a scalar or a scalar and a JSON value for equality by converting the
    scalar to a JSON value and comparing both JSON values according to 1.

docs/mkdocs/docs/api/basic_json/operator_lt.md

@@ -15,7 +15,8 @@ bool operator<(ScalarType lhs, const const_reference rhs) noexcept(/* see below
   following rules:
     - If either operand is discarded, the comparison yields `#!cpp false`.
     - If both operands have the same type, the values are compared using their respective `operator<`.
-    - Integer and floating-point numbers are automatically converted before comparison.
+    - Integer and floating-point numbers are compared by their exact values, without converting the integer to
+      floating-point. For instance, `9007199254740992.0` is less than `9007199254740993`.
     - In case `lhs` and `rhs` have different types, the values are ignored and the order of the types
       is considered, which is:
         1. null

docs/mkdocs/docs/api/basic_json/operator_spaceship.md

@@ -12,10 +12,8 @@ std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see be
     - Two JSON values compare with a result of `std::partial_ordering::unordered` if either value is discarded.
     - If both JSON values are of the same type, the result is produced by 3-way comparing their stored values using
       their respective `operator<=>`.
-    - Integer and floating-point numbers are converted to their common type and then 3-way compared using their
-      respective `operator<=>`.
-      For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to
-      floating-point with the second value.
+    - Integer and floating-point numbers are 3-way compared by their exact values, without converting the integer to
+      floating-point. For instance, `9007199254740993` compares greater than `9007199254740992.0`.
     - Otherwise, yields a result by comparing the type (see [`value_t`](value_t.md)).
   
 2. 3-way compares a JSON value and a scalar or a scalar and a JSON value by converting the scalar to a JSON value and

docs/mkdocs/docs/api/basic_json/patch.md

@@ -45,7 +45,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
   `"unresolved reference token '-'"`.
 - Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) if JSON pointer has no parent
-  ("add", "remove", "move")
+  ("remove", "move")
 - Throws [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) if an "add" operation's target
   location has a parent that is neither an object nor an array.
 - Throws [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) if a "remove" operation's target

docs/mkdocs/docs/api/basic_json/patch_inplace.md

@@ -41,7 +41,7 @@ No guarantees, value may be corrupted by an unsuccessful patch operation.
   pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
   `"unresolved reference token '-'"`.
 - Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) if JSON pointer has no parent
-  ("add", "remove", "move")
+  ("remove", "move")
 - Throws [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) if an "add" operation's target
   location has a parent that is neither an object nor an array.
 - Throws [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) if a "remove" operation's target

docs/mkdocs/docs/api/macros/json_use_legacy_discarded_value_comparison.md

@@ -18,7 +18,8 @@ When enabled, comparisons involving at least one discarded JSON value yield resu
 | `>=`         | `#!cpp true`  |
 | `>`          | `#!cpp false` |
 
-Otherwise, comparisons involving at least one discarded JSON value always yield `#!cpp false`.
+Otherwise, comparisons involving at least one discarded JSON value yield `#!cpp false`, except for `!=`, which is the
+negation of `==` and yields `#!cpp true`.
 
 ## Default definition